This project is designed to investigate the general question of how the small blood vessels contract. The specific aims are: to record and compare electrical activity from the small vessels and to see how it is modulated by neural input, exogenous transmitters and gastrointestinal peptides; to determine the degree of control of mechanical activity by electrical activity; and, to investigate the mechanism of electrically and nonelectrically triggered contractions by measuring intracellular calcium levels. Intracellular electrical methods and optical mechanical methods will be used. Calcium levels will be measured with the aequorin method. Arteries less than 100 Mu and veins less than 200 Mu diameter will be studied. Studies will be confined to canine gastric submucosal vessels in vitro. The small vessels are important because they are major determinants of peripheral resistance and play a major role in regulating fluid exchange and blood distribution and yet we know far less about the small vessels than we do about the large vessels. Their normal function and how they malfunction may be the key to understanding peripheral vascular spasm. The vessels which travel through the submucosa are of special interest because they affect the distribution of blood between the mucosal and muscle layers in the gut and are of special interest with respect to mesenteric vascular disease.